1. Field of the Invention
The present invention relates to an electric motor which is used in an electric power steering apparatus or the like.
2. Description of the Related Art
An electric power steering apparatus, as described in Japanese Patent Application Laid-open No. H9-84300, assists steering effort which a driver applies to a steering shaft, by connecting an assist shaft of a steering gear to a rotation shaft of an electric motor and transmitting a rotation force of the electric motor to the steering gear.
A conventional electric motor, as described in Japanese Patent No. 3207177, is constituted by a tubular yoke, a rotation shaft rotatably provided within the yoke, a stator provided with a magnet fixed within the yoke, a rotor fixed to the rotation shaft and inserted to an inner side of the stator, a brush brought into contact with a commutator of the rotor, a brush holder holding the brush and connected to the yoke, and a plurality of electric conductors buried in the brush holder and feeding an electric current to the brush via a pigtail.
In the conventional art, two electric conductors forming two respective poles (+side and xe2x88x92side) are buried within an inner narrow limited range in a diametrical direction from an inner diameter position of the yoke in the brush holder. This structure results in difficulty of arrangement of the electric conductors.
In order to arrange two electric conductors on one surface without being in contact with each other in the interior of the brush holder, it is necessary to prepare a wide burying range, and it is necessary to increase an inner diameter of the yoke, so that an outer diameter of the electric motor is increased. In order to prevent the electric motor from becoming undesirably large, it is necessary to shift surfaces on which two electric conductors are arranged from each other, so that the electric conductors are formed in a stereoscopically complex shape, and further, a bending process would be required. Accordingly, the cost becomes high.
An object of the present invention is to improve an arranging property of the electric conductors buried in the interior of the brush holder without increasing the outer diameter of the electric motor.
According to the present invention, there is disclosed an electric motor having a tubular yoke. A rotation shaft is rotatably provided within the yoke, and a stator is provided with a magnet fixed within the yoke. A rotor is fixed to the rotation shaft and is inserted to an inner side of the stator. A brush is brought into contact with a commutator of the rotor. A brush holder is arranged to hold the brush and is connected to the yoke. A plurality of electric conductors are buried in the brush holder and are arranged to feed an electric current to the brush.
A protruding portion protruding to an outer side in a diametrical direction from an inner diameter position of the yoke is provided in the brush holder, and at least a portion of the electric conductor is buried in the protruding portion.